Devices for stacking sheets of material, such as sheets of corrugated material, are well known. One example of a commercially available device is the AGS2000 Rotary Die Cut Stacker made by the assignee of the present invention, A.G. Machine, Inc., Weyers Cave, Va. Further examples of such devices are disclosed in U.S. Pat. No. 3,321,202 to Martin and U.S. Pat. No. 3,419,266 to Martin, each of which is expressly incorporated by reference in its entirety.
FIGS. 1 and 2 illustrate a conventional apparatus for stacking corrugated blanks. As seen there, the stacking machine 100 generally comprises a layboy section 102 which receives corrugated blanks, such as those produced by a rotary die cut machine (not illustrated), and discharges the corrugated blanks onto a transfer conveyor 104. The transfer conveyor 104 receives the blanks and transports them to a main conveyor 106. The main conveyor 106 has an intake end 108 and a discharge end 110. At its intake end 108, the main conveyor 106 is mounted to a base 112 at a pivot point 114 so that the conveyor may be pivoted to raise the discharge end 110 of the conveyor 106. At the discharge end 110 of the conveyor 106, an accumulator section 116 receives discharged blanks.
In operation, the main conveyor 106 is pivoted about the pivot point to lower the discharge end 110 of the conveyor to an initial position. (The illustrated position illustrates the conveyor raised to an upper position.) Sheets are fed onto the main conveyor 106 at its intake end 108, transported along the distance of the conveyor to its discharge end 110, and discharged from the conveyor. The sheets are discharged with sufficient momentum to strike a backstop 118 in the accumulator section 116 that stops the forward momentum of the sheets. The stopped sheets settle down, typically onto a discharge conveyor, to form a stack of sheets. As additional sheets are placed on the stack, the main conveyor 106 is pivoted to raise the discharge end vertically so that the discharged sheets are stacked one by one.
Once a stack of sheets is completed, to permit time to carry the stack of sheets away without stopping the machine, the accumulator section 116 is activated by activating catcher elements 120. The catcher elements 120 hold sheets in the accumulator section while the previously formed stack is removed. After the stack is removed, the main conveyor 106 is lowered and the accumulator section 116 is deactivated by withdrawing the catcher elements 120. The accumulated sheets are dropped to form a new stack of sheets.
One drawback to conventional stackers such as this is that the discharged sheets sometimes become interlocked and jammed in the accumulator. This occurs partially because the angle of discharge of the conveyor varies. When the main conveyor is placed at the position shown in FIG. 1, that is, an upper position, the conveyor has an angle θ1 with respect to horizontal. Sheets are discharged from the conveyor at the same angle as the angle of the conveyor, and, therefore, in the upper position, sheets are discharged with some upward momentum. On the other hand, when the main conveyor is lowered to the initial position described above, the angle θ1 is 0°, or even negative, with the conveyor 106 angled down with respect to horizontal. Discharged sheets therefore have either no upward momentum, or may even have downward momentum. This variation in the momentum of discharged sheets affects the seating of sheets into the accumulator section.
There have been attempts to address this issue, and one common method is the use of forced air. Forced air is blown underneath a discharged sheet to form a cushion so that discharged sheets settle more uniformly. Forced air has proven to be useful, yet it also has drawbacks. The forced air can vary in intensity and location, thereby preventing blanks from being adequately diverted. Furthermore, the trajectory and force of the air is not always sufficient to assure that sheets are properly seated into the accumulator.
Accordingly, there is a need for an improved apparatus for stacking sheets that guides corrugated blanks into an accumulator in a manner that minimizes, or prevents, interlock jamming in the accumulator.